1. Field of the Invention
This invention relates to a vehicular apparatus and method for determining the centripetal force of a vehicle. More particularly, the present invention relates to an apparatus and method for dynamically determining the centripetal force of a vehicle requiring only the measurements of vehicle speed and steering force.
2. Disclosure Information
When a moving vehicle negotiates a turn, the centripetal force of the vehicle attempts to keep the vehicle in its circular path while inertia forces urge the vehicle to continue in a straight line. During the turn, the center of gravity of vehicle begins to accelerate in a lateral direction generally perpendicular to the longitudinal axis of the vehicle. Friction between the vehicle road wheel and the surface upon which the vehicle travels acts to keep the vehicle in the turn. However, at a given vehicle velocity, if the inertia acting on the turning vehicle exceeds the centripetal force required to keep the vehicle in the turn and the lateral acceleration of the vehicle exceeds the friction forces between the road wheels and the road, the road wheels begin to slip away from the direction of the turn, creating a potentially dangerous condition and requiring responsive action from either automatic systems within the vehicle or from the vehicle operator. It is therefore desirable to determine the centripetal force of the vehicle to initiate responsive actions of the vehicle before the threshold value is exceeded and a potentially dangerous situation is encountered. Typical responsive action may be the employment of a traction control system or an antilock braking system or the indication to the driver of a warning device within the vehicle.
Furthermore, when the lateral acceleration of the vehicle exceeds a predetermined limit, the vehicle undergoes undesirable body roll, thereby redistributing the weight of the vehicle toward the wheels that are radially outward of the steering center of the vehicle. When both the front wheels or both rear wheels are deflected by roll, the roll-steer effect can be pronounced. The result is a vehicle which is less comfortable for the occupants of the vehicle. It is also desirable to determine the lateral acceleration or centripetal force of the vehicle so that variable rate shock absorbers or an active or semi-active suspension system can be employed prior to exceeding a predetermined limit to negate these undesirable affects of body roll.
Many systems have been proposed which determine when a predetermined limit related to the road tire adhesion of a vehicle has been exceeded. For example, my U.S. Pat. No. 4,882,693 discloses a system for determining the road adhesion of a tire installed on a road wheel of a vehicle operating on a road way. The system uses a turn angle sensor, a vehicle velocity sensor and a steering force sensor to determine when a predetermined road adhesion value has been exceeded. The turn angle sensor of the '693 patent is used in conjunction with a find center algorithm to determine the center steering position of the steering wheel used to determine when the vehicle is turning. However, during long turns, such as during a cloverleaf turn onto a freeway, the steering angle sensor may assume an incorrect center steering position and thereby miscalculate whether the vehicle is turning. If such a mistake occurs, the vehicle will not assume that any centripetal force or lateral acceleration is acting on the vehicle and responsive actions will not be initiated. Furthermore, if the vehicle is traveling on a low coefficient of mu surface, such as ice, a vehicle operator may be turning the wheel rapidly but minimal centripetal force is developed on the car. In such a case, the '693 system may initiate responsive action, such as the switching of the shock absorbers to a firm setting to counteract body roll when in fact no body roll is present and no switching necessary due to the low mu surface. It is desirable to keep the vehicle shock valving in a soft setting when traveling on low coefficient of friction surfaces and prior to any centripetal force buildup so that roadwheel traction is increased and vehicle steerability is not degraded. Therefore, there is a need to develop a system which does not rely on a turn angle sensor to determine the centripetal force of a vehicle. Other systems also propose the use of a turn angle sensor to determine road responsive conditions acting upon the vehicle. For example, U.S. Pat. Nos. 4,621,833; 4,629,025; 4,652,010; 4,660,853; 4,666,013; 4,687,223; and 4,747,055 all rely on turn angle sensors and are subject to the same potential miscalculations as the '693 patent.
Other systems have been proposed which utilize various operating parameters in determining whether to initiate responsive action. For example, U.S. Pat. No. 4,463,936 discloses an apparatus for controlling the friction between the leaf springs of an automobile. The apparatus relies solely upon the pressure developed in the power steering assembly to determine whether to clamp the leaf springs to alter the ride of the vehicle. The apparatus does not utilize vehicle speed as a parameter in determining whether to clamp the leaf springs, resulting in degraded vehicle ride quality when unnecessary clamping of the vehicle occurs due to steering maneuvers at low speeds, such as during parallel parking or other parking lot maneuvers. Other proposed systems rely on other various parameters such as U.S. Pat. Nos. 3,552,517 and 4,796,720 in determining when to initiate responsive action.
U.S. Pat. Nos. 3,893,330; 4,050,290; 4,212,063; and 4,779,447 as well as Russian Patent No. 1153-273 all disclose systems for determining the coefficient of friction between the road wheels of the vehicle and the surface upon which the vehicle is traveling and all rely on various vehicle operating parameters. None of these patents disclose a system for determining centripetal force exerted on a vehicle as will be discussed below. Furthermore, none of these patents teaches or suggests the use solely of the vehicle parameters of vehicle velocity and steering force in determining the centripetal force or lateral acceleration of the vehicle. Therefore, vehicle speed is a necessary parameter to consider when determining the centripetal force or lateral acceleration of a vehicle.
The present invention solves the above problems by utilizing only the parameters of vehicle velocity and force to determine the centripetal force on the vehicle.
It is an advantage of the present system that the ability to determine centripetal force is not effected by tire wear or by the type of tire employed.
It is a further advantage of the present invention that a centripetal force measuring system according to this invention could be used in conjunction with a driver warning system, a brake control system, a suspension control system, a vehicle speed control system, a steering gear power assist control system, or yet other types of vehicular systems.
It is a still further advantage of the present system that this system can compensate for different loading conditions of the vehicle, since the mass of the vehicle directly relates to centripetal force exerted on the vehicle.
Other objects, features, and advantages of the present invention will become apparent to those skilled in the art to which this invention pertains.